Envoy: Set original destination cluster cleanup interval to 1.5 seconds.
Envoy: Set original destination cluster cleanup interval to 1.5 seconds.

Envoy keeps upstream connections open for later reuse, which helps
avoid unnecessary TCP handshake roundtrips.  Unfortunately this breaks
down when a policy change changes the real destination of those
connections, e.g., redirecting the connection to a proxy.  In this
case the connection does not work any more, as the new destination
does not have the right connection state.

Orignal destination clusters can open unlimited number of upstream
connections, as the set of upstream hosts is not limited by
configuration.  In order to limit resource use, original destination
clusters periodically scan all the previously used destination hosts
and removes the ones that have not been used for upstream traffic
since the last period.  This period between the cleanups is
configurable and defaults to 5 seconds. This is too long for some of
the Cilium runtime tests, that repetitively issue traffic between
endpoints, but change the network policy in between.

Changing the cleanup interval to 1.5 seconds seems to allow these
tests to pass correctly, while still allowing re-use of the upstream
connections in cases where the gap between requests is no longer than
1.5 seconds.

Signed-off-by: Jarno Rajahalme <0f1ab0ac7dffd9db21aa539af2fd4bb04abc3ad4@covalent.io>

eloycoto/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,scanf/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,scanf/cilium,eloycoto/cilium,eloycoto/cilium,tgraf/cilium,tklauser/cilium,scanf/cilium,scanf/cilium,eloycoto/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,cilium-team/cilium,cilium/cilium,cilium-team/cilium,michi-covalent/cilium,scanf/cilium,scanf/cilium,cilium/cilium,eloycoto/cilium,tgraf/cilium,scanf/cilium,eloycoto/cilium,tgraf/cilium,eloycoto/cilium,cilium/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium